How should a company respond if a consumer politely asks it to stop tracking his or her behavior on the company’s website?

And what role should a browser play in helping consumers communicate their preferences regarding online tracking?

These are increasingly tough question for Internet giants like Google and Facebook, who stand to lose millions, perhaps billions, of dollars if consumers successfully limit online tracking. Currently, consumers can request a company stop tracking them online by changing a setting in their browser or by adding a browser plugin. But companies frequently ignore these requests.

During a Wednesday session at the annual RSA security conference in San Francisco, spokespeople from Google and Facebook explained that they are not responding to “do not track” requests because it isn’t clear that consumers know what “do not track” means.

Keith Enright, a senior policy counsel at Google, said there is a “consumer confusion question” that is caused by the fact that there is still no official, industry-accepted “Do Not Track” standard. Acknowledging a consumer’s “do not track” preference “in some ad hoc way” may not be meeting that user’s expectations, Enright explained.

Erin Egan, the chief privacy officer of Facebook, said she also wasn’t sure that a “do not track” setting on a browser actually reflected a user’s desire not to be tracked, especially in cases where a company like Facebook was tracking users in order to customize their web experience, rather than to sell advertising. “For Facebook, we have social plugins,” she explained. “We don't use that data for an advertising purpose, we use it to personalize the data on those page.”

Until there is an official standard set by the World Wide Web Consortium (W3C), “it’s really hard for companies like us,” Egan said.

This week, Microsoft and Mozilla made it harder. On Tuesday, Microsoft released Internet Explorer 10 for Windows 7 which includes a “do not track” setting turned on by default. Explorer 10, with the “do not track” default, was released for Windows 8 in late October, despite fierce objections from the online marketing industry who argued, among other things, that it would “kill free speech.”

Meanwhile, Mozilla, which kicked off the whole "do not track" discussion two years ago by allowing its users to turn on a “do not track” setting in the Firefox browser, said it would start blocking third-party cookies in a new version of the browser that has been released for developers. The feature could ultimately be included in a general browser release, following a standard vetting process.

Alex Fowler, Mozilla’s chief privacy offer, said the feature is a response to a huge explosion in third-party cookies. “This is about user expectations,” he explained, noting that 14 percent of Mozilla’s users have enabled the “Do Not Track” setting.

“We have tried to engage with the industry for many years,” Fowler said. “We are seeing an incredible expenditure of money and talent to refine the tracking ecosystems and we are not seeing the same comparable investment in controls that are meaningful to the user.”

Fowler described how he visited four sites on Monday morning and received over 300 cookies from 120 companies.

Mike Zaneis, the general counsel of the Internet Advertising Bureau, tweeted on Saturday that Mozilla’s move was “a nuclear first strike against ad industry.”

Fowler countered that Mozilla is merely doing what Safari has been doing for years. “Mozilla’s users frequently express concerns about web tracking, and we’ve been listening,” he wrote in a blog post. "We have a responsibility to advance features and controls that bring users’ expectations in line with how the web functions for them."